This application claims the benefit of Korean Application No. P2000-85759, filed on Dec. 29, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an advanced mobile communication system and, more particularly, to an apparatus and a method of transmitting and receiving one or more ATM cells in an ATM network-based mobile communication system.
2. Background of the Related Art
In general, a typical mobile communication system includes a mobile station (MS), a base station (BS), a Base Station Controller (BSC), and a Mobile Switching Center (MSC). The system usually handles messages related to three types of call traffic: a voice call, a data call, and a voice/data call. The traffic messages travel between the MS and the BS, the BS and the BSC, and the BSC and the MSC, respectively. The base station is connected to the BSC with an E1 line, and the BSC is connected to the MSC with a Synchronous Transfer Module 1 (STM-1) line.
When the mobile communication system operates in an Asynchronous Transfer Mode (ATM) network system, the traffic messages, mentioned above, are transmitted in the form of ATM cells. In other words, one or more ATM cells travel between the BS and the BSC or between the BSC and the MSC.
In general, the ATM Adaptation Layer (AAL) provides support for higher-layer services such as signaling, circuit emulation, voice, and video. AALs also support packet-based services, such as IP, LANs, and frame relay.
There are four different types of the currently standardized AALs: AAL1, AAL2, AAL3/4, and AAL5. First of all, AAL2 supports ATM transport of connection-oriented Variable Bit Rate (VBR) packetized voice and video. On the other hand, the Common Part (CP) AAL5 supports both connection-oriented and connectionless VBR traffic. Support for connectionless or connection-oriented service is provided at the Service Specific Convergence Sublayer (SSCS) level. However, despite the simplicity of AAL5, AAL5 is now coming under criticism for its relatively inefficient operation, especially for the mix of packet sizes typically used on the Internet.
To use the connection lines of the system more efficiently, the control messages travel in the form of AAL5-type ATM cells (hereinafter, “AAL5 cells”). On the other hand, the traffic messages, including user data, travel in the form of AAL2-type ATM cells (hereinafter, “AAL2 cells”) in the ATM network system.
The BS interface, included in the BSC, initially receives AAL2 cells from the BS and subsequently generates AAL5 cells, corresponding to the received AAL2 cells. Then the BS interface sends the AAL5 cells to the main switch element, which is also located inside the BSC. A single AAL5 cell can include only one set of user data. In other words, if a set of user data is too large, so that it needs to be divided into many data subsets, the number of AAL5 cells that need to be generated must be identical to the number of data subsets. Therefore, we may conclude that this is a very inefficient way to transmit user data having a large size.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.